All things G1176 - the new "repost" thread.

[skal1]

cheers gswan,

now where is that tx thread.


skal1

 

[aclac]

yeah i had another go at it  and i had to change the meter i was using because it did not have a  1db ref , went through the calibration again and now the attack is working as it should be , those bf245 have a very tight working window might have to change the 1 turn pot for a multi.

Yes, the Qbias is very sensitive. If you plot the FET characteristics first it will give you an idea of where the optimum point would be and how sensistive it is. A 25 turn pot is a good idea for this adjustment.

Bear in mind that there will be some thermal dependancy in the FET adjustment, so don't calibrate it in freezing conditions and expect it to be the same on a hot day!

I calibrated mine last winter, when humidity was dry and temperature was 3 degrees less... It must recalibrate now, because it compress all the time, when relase is somewhere left (slow). I noticed earlier when I calibrated first time, that when I blow little bit into PCB, then strong compression start and step slowly back after couples of seconds... So, don't breath inside the PCB- "room"!

 

[gswan]

I calibrated mine last winter, when humidity was dry and temperature was 3 degrees less... It must recalibrate now, because it compress all the time, when relase is somewhere left (slow). I noticed earlier when I calibrated first time, that when I blow little bit into PCB, then strong compression start and step slowly back after couples of seconds... So, don't breath inside the PCB- "room"!

That sounds a little too sensitive.
Did you measure and plot the FET characteristics? You may find that your FET is a bit out of spec, and you are well into the linear conduction region even with the GR turned off.

 

[ruckus328]

Hey guys, I was hoping somebody might be able to tell me.  I'm going to start building an 1176 soon, Mnat's Rev D Boards, my question of how deep of a 2U enclosure I should get?  I need to order a couple 1U's for my GSSL's now but don't want to have to place another order later for the 1176, so figured I just get that enclosure now also.

Is 8" (203mm) too shallow?

The next size up is 11" (280mm), but don't want to go bigger than I have to.

 

[Chrome Heart]

Hey guys, I was hoping somebody might be able to tell me.  I'm going to start building an 1176 soon, Mnat's Rev D Boards, my question of how deep of a 2U enclosure I should get?  I need to order a couple 1U's for my GSSL's now but don't want to have to place another order later for the 1176, so figured I just get that enclosure now also.

Is 8" (203mm) too shallow?

The next size up is 11" (280mm), but don't want to go bigger than I have to.

I used 8" for the pair Ive done and it worked fine. Theres plenty of room.

 

[pearldrum944]

EDIT: I figured out my fuse issue (fast acting instead of slow blow)

On one of my units, I only get the GR meter to work when in SLAM mode, compression is working.  When in any other ratio the GR meter is resting on the left.  

+4 and +8 seem to work fine.  Any ideas?

These are mnats rev D with hairball kits.

 

[pearldrum944]

Bump?  I have been searching but am still lost.

 

[ricothetroll]

Hi !

I have a problem with my G1176 : at Q2's collector Q2 (first transistor of the preamp section) the signal is very saturated (some kind of non symetrical square wave). The signal is already slightly saturated at Q2's base.

I did the following measures :

On top of R18 : 23.9 V

Q2 : C = 1.58 V
      B = -1.14 V (!!!)
      E = 0.04 V

Q3 : C = 7.41 V
      B = 1.59 V
      E = 1.47 V

Q4 : C = 29.3 V
      B = 7.4 V
      E = 13.3 V

I removed the FET (Q1) to get rid of the sidechain influence.

I have no idea about what could be the cause of such weird voltages, so any clues are welcome !

Thanx in advance.

Best regards.

Eric

 

[pearldrum944]

No matter the level of the input, any time I turn my output knob past 6 (4 o'clock) I get a pop then some buzz, the GR meter drops about 4db or so in slam mode.  My GR meter is not working in the other ratios, but when there is buzz the meter jumps to -5 instead of resting on the left.  If the compressor is in GR off mode, the GR meter in slam jumps to +2 instead of going down to -3 or -4 when I have the buzz.  Think the buzz issue is related to how my meter is not working in GR mode for the other ratios? 

 

[gswan]

I did the following measures :

On top of R18 : 23.9 V

Q2 : C = 1.58 V
       B = -1.14 V (!!!)
       E = 0.04 V

Q3 : C = 7.41 V
       B = 1.59 V
       E = 1.47 V

Q4 : C = 29.3 V
       B = 7.4 V
       E = 13.3 V

Check the orientation of Q2, Q3 and Q4. Also check all resistors around these transistors.

 

[ricothetroll]

Hi Gswan,

Thanx for your answer !

Well I guess you're right, at that step all I have to do is to be courageous and desolder - check - resolder that whole section ! It could be a bad solder too after all (I double checked the transistors and I always measure every resistor before soldering it the first time).

To be continued...

Best regards.

Eric

 

[gswan]

Well I guess you're right, at that step all I have to do is to be courageous and desolder - check - resolder that whole section ! It could be a bad solder too after all (I double checked the transistors and I always measure every resistor before soldering it the first time).

That would be one way to do it, although it sounds like the hard way to me.
Check first, visually, with data sheets for the transisor pin configuration and colour codes for the resistors. Confirm that all looks OK visually. Check Vbe of the transistors, which in this case should all be about 0.5-0.8V.

 

[pearldrum944]

Okay, as far as I can tell I have 2 properly working mnats/hairball rev d's, except the GR meter.  +4 and +8 work fine, but on BOTH units the GR meter only works in slam mode (or with any ratio combination that at least has 1:4 and 1:20 pushed in simultaneously).  This has got to be something I am doing wrong since both units have the issue, but I have checked my wiring over and over again, resoldered the meter/ratio boards. and double checked that all of my resistors are correct in the GR meter driver section.  What am I missing?  What is it about changing the ratio that affects the GR meter's reading? ???

 

[gswan]

What is it about changing the ratio that affects the GR meter's reading? ???

The amount of bias applied to the GR metering FET.

 

[pearldrum944]

Okay, thanks...that was easier than I thought!  So adjusting my Q bias control I was able to get the meter to come back up for GR.  But now when I am trying to calibrate, I can't get my -1db of Q bias adjustment without the GR meter dropping back down to where the needle does not move and r71 is not able to bring it back up.

 

[ptmoore37]

Quick (probably dumb) question for a Rev J board...

Checking my negative voltage rail (r85), i'm getting -12.85v on the OTHER side of r85.  I'm getting -.04v on the side of the resistor that needs to be measured (as indicated on the PC board).  All diodes are soldered in the correct direction and seems like no caps have been switched around. 

I know it's something simple, that's why I'm asking rather than ripping up my entire PS section.

 

[ward]

It's probably best to go over it following the schematic.
Going from transfo to -10V point.
Measure after CR10 and CR9 (recheck polarity),
(check the polarity of c24 and c26)
after R86 and then after R85.

 

[gswan]

Quick (probably dumb) question for a Rev J board...

Checking my negative voltage rail (r85), i'm getting -12.85v on the OTHER side of r85.  I'm getting -.04v on the side of the resistor that needs to be measured (as indicated on the PC board).  All diodes are soldered in the correct direction and seems like no caps have been switched around. 

I know it's something simple, that's why I'm asking rather than ripping up my entire PS section.

Sounds like you have a short circuit on your -10V rail. Check with an ohm meter with power off. Then trace it out to find the short.

 

[rooster21]

yes I have, but I would like to redo it just to be sure. Some clarification on the procedure would be nice.

Measurements:
1. GR bias wound out
2. Release fully CW
3. Attack off (GR disabled)
4. Apply a 0.775Vrms 1kHz sine wave to the input.
5. Adjust the input and output controls so that the output of each stage is not clipping
6. Measure the input and output AC voltage values

these where the instructions i followed but I would like to verify the folowing:

1. GR wound out meaning ccw (least resistance) or cw (most resistance), I'm assuming least.
4. .775Vrms, this means roughly .39Vrms on pin 2 and 3 respectively, right?
5. should the input and output be adjusted to the maximum before audible distortion?

For the gain tests you need to have the GR FET disabled, ie the Qbias trimmer set to where the FET is not conducting (most -Ve value on the FET Vgs).

Apply a signal to the input (the actual value is not important, somewhere around 100mV to 1V RMS should do). It's a balanced input so the signal goes across pins 3 and 3 of the XLR connector.

Now measure the signal value at the top of the output pot and wind the input pot up until you get a few Vrms there. Measure the input to this stage (input pot wiper) and calculate the gain. Do the same thing for the output section.

Sorry it's taken me so long to reply, but I've had a really hard time trying to make sure that the GR FET is not conducting. I've taken some time to attempt to understand Vgs a little better. If I'm not mistaken, I should have the negative probe of my DMM on the gate of the FET, and the positive probe on the source, and when I change the trimmer for Qbias the result on the DMM (V ac) should change, correct? No matter what I change I get a fixed .012 Vac.

To provide some more info I'm using the 2N5457 provided from Hairball, and they are installed mirror to the PCB which is correct, all the resistors have been verified as correct values and  several solder joints have been reheated. Could someone enlighten me as to what I'm doing wrong?

Thanks
GdS

 

[gswan]

Sorry it's taken me so long to reply, but I've had a really hard time trying to make sure that the GR FET is not conducting. I've taken some time to attempt to understand Vgs a little better. If I'm not mistaken, I should have the negative probe of my DMM on the gate of the FET, and the positive probe on the source, and when I change the trimmer for Qbias the result on the DMM (V ac) should change, correct? No matter what I change I get a fixed .012 Vac.

Yep, you are mistaken.
You should be measuring a DC voltage from the gate to GND. It should range from about -2.5V up to 0V.
When it is most -ve, it should be past the pinchoff voltage and not conducting.